A new chart from the Institute for Women's Policy Research (IWPR) estimates that, at the current pace, the gap in pay between men and women won't be closed until 2057.

The chart, which looks at full-time, year-round workers in the United States, shows women's median earnings as a percent of men's median earnings. It uses actual data from 1960 through 2011, then projects forward through 2060.

In the 1960s, women's earnings were generally just shy of 60 percent of men's earnings. In 2012 that number had increased to more than 80 percent. That's a significant improvement, but still leaves a substantial pay gap between women and men. ABC/Univision recently detailed a number of reasons for that gap, from discrimination to declining employment opportunities. For more information, go here.

The chart might look dismal, but the real situation could actually be worse than it predicts. According to Jeff Hayes, a study director with the think tank, the 2057 estimate is optimistic.

Hayes said that progress hasn't been a straight line, and that while the wage gap shrank in the 1970s and '80s, that progress slowed in the '90s and tapered off in the 2000s. To reach pay equity by 2057, the current rate of progress would have to remain steady, and that's looking less likely.

He added that some of the acceleration in the '70s and '80s in fact had to do more with men's wages stagnating than women's wages improving.

Pay won't truly be equal until "we make measurable changes," he said, such as passing policies aimed at ending occupational segregation, which results in a disproportionate concentration of men in high-paying, high-status jobs. Women are still more likely to gravitate toward lower paying jobs and to take time off after having a baby than men, which can sometimes slow their ascendance up the career ladder.

The issue has gained widespread media attention recently, with Facebook Chief Operating Officer Sheryl Sandberg authoring "Lean In," a bestselling book that encourages women not to give in to societal pressure to be nice or demure in ways that limit their ability to tackle career advancement opportunities.

The National Committee on Pay Equity, a coalition of advocacy organizations aimed at ending wage inequality, has declared this coming Tuesday to be Equal Pay Day. The committee launched the annual Equal Pay Day in 1996 to raise awareness about the gap between men's and women's wages. The group wrote online that they chose April 9 because that's "how far into 2013 women must work to earn what men earned in 2012."

But the wage gap issue is complex, and a variety of attempts to eliminate it have fallen short -- and not just in the United States.

"While I think we could do better," Hayes said, "when you look around the world, no one country has solved this. It's still fairly universal."